US Secretary of State Hillary Clinton hit back on Thursday at a Russian threat to deploy weapons in response to a NATO missile shield as the two sides failed to defuse a rift over the US-backed system.

“We will continue to press forward on missile defence,” Clinton told a press conference in Brussels after talks between NATO foreign ministers and their Russian counterpart Sergei Lavrov.

“It does not affect our strategic balance with Russia and it’s certainly not a cause for military counter-measures,” she said.

Despite the disagreement, the two sides agreed to forge ahead with negotiations on cooperating in the system but Lavrov warned that time was running out.

Seeking to allay Russian fears that the defence system to be deployed partly in former Soviet bloc countries will undermine Russia’s strategic arsenal, Clinton said it was mainly aimed at countering a threat from Iran.